The common hearing aid of today is a digitally programmable hearing aid comprising a microphone, a signal processing device and a receiver. The hearing aids are sold with only one predetermined type of receiver. Adaptation of the hearing aid to the needs of the hearing impaired is performed by programming the signal processing device of the hearing aid. For the adaptation, the hearing loss can be categorized in different levels of severity. Different levels of severity require different degrees of the output sound pressure level of the receiver. During programming of the hearing aid the degree of amplification in the signal processing device is set to provide a certain degree of output sound pressure level of the receiver. However, the maximum output sound pressure level is a property of the receiver that is built into the hearing aid. To be able to use the hearing aid for any level of severity of the hearing loss, a receiver with a very high maximum output sound pressure level has to be used. The use of a receiver with a lower maximum output sound pressure level would be less expensive. Furthermore, different dynamic ranges are preferable for different degrees of severity of the hearing loss, also with regards to the quality of adaptation of the hearing aid to the needs of the hearing impaired user. Accordingly, the use of only one predetermined receiver has the drawback that the hearing aid can not be adapted to a wide variety of severity of the hearing loss with a maintained level of quality.
From US 2002/0026091 A1 and from U.S. Pat. No. 6,712,754 B2 implantable hearing systems comprising a transducer for communicating vibrations to the ossicular chain are known. The described hearing aids comprise impedance measuring means for measuring the mechanical impedance of a biological load structure which, upon implantation of the output transducer, is coupled to the output transducer. The measured impedance is not a characteristic parameter of the transducer itself.
From U.S. Pat. No. 6,934,400 B1 a hearing aid comprising a signal processing unit and an electric/mechanical transducer is known wherein the impedance of the transducer can be switched to different levels to adapt the dynamic range of the hearing aid to different situations. However, the described hearing aid has the drawback that the structure of the transducer is rather complicated, needs much space and is expensive.
In recent years a the type of hearing aids have become increasingly popular, namely where the receiver part of the hearing aid is placed in the ear canal and the remaining hearing aid parts are placed in a housing behind the ear lobe of the hearing aid user. In this type of hearing aid the receiver may easily be exchanged, and here it is important that the receiver which is used is in line with the settings or contents of the behind the ear part of the hearing aid.
As the market for Receiver in the Ear (RITE) hearing aids (HA's) increases, more RITE modules with different receivers will come to co-exist in the coming years. A strategy for identifying and distinguishing these RITE modules is needed to ensure that future HA solutions will not impose damage and/or produce uncomfortable sound levels to the end user in case of attaching a wrong RITE module, e.g. one with higher sensitivity than expected during fitting.
WO 02/11509 describes a hearing device comprising a first module with an electrical supply as well as an electrical to mechanic output converter and a second module with a signal processing unit as well as an acoustical/electrical input converter. In an embodiment, the hearing device comprises a code unit in said first module and a code-reader and decoding unit in said second module. WO 99/09799 deals with a hearing aid with a central signal processing unit, which interacts with peripheral units on the input and output side. The peripheral units each have an identification unit whose output interacts with the input of a comparing unit. The comparing unit in turn interacts with identification-possibility memory units, and acts on a configuration storage unit on the output side. In this way, the hearing aid configuration can identify itself using the peripheral units.